Tracker dropdown is missing in the Tracking settings (in Movie clip editor)
This option was removed in 2.64:


  First, the old option called Tracker was eliminated. The old Hybrid tracker
  was doing exactly the same as the SAD tracker, with the exception that
  it could do more accurate subpixel precision tracking by following the
  brute-force search with a subpixel refinement. The SAD tracker was
  also limited in that it only worked on 8-bit images and is unsuitable
  for 32-bit float images like those used in Mango.
  
  Secondly, the KLT tracker with its pyramid tracking helped tracking
  blurry footage, but could be quite useless when the background texture
  was moving in the opposite direction of the feature point. In such
  cases the Hybrid tracker was much better than KLT, and for this reason
  the KLT tracker was made obsolete.


In other words, the SAD and KLT options were replaced with a improved hybrid tracker with new options. 

From the wiki:


  The new tracker is a unified algorithm with more options, and
  specifically some options to make it work exactly the same as the old
  non-planar Hybrid tracker. The options are:
  
  
  Motion Model defines which possible motions tracking feature has. Currently supported models are: Location only, Location+Rotation,
  Location+Scale, Location+Rotation+Scale, Affine and Perspective. This
  option should be set depending on which motion a particular feature
  has and it'll make tracking most accurate for such a motion.
  Perspective is usually used to track a planar feature, but often
  Affine is a good enough approximation and may have more stable tracks.
  Prepass enables a two pass tracking, where the first pass is a brute force tracking of location only, and the second pass will use
  tracking of the full motion model refining the first pass. To get
  behavior that is almost identical to the Hybrid tracker in previous
  Blender versions, enable Prepass and set the motion model to Location
  only.
  Normalize means patterns will be normalized by their average intensity while tracking, to make them invariant to illumination
  changes. An example where this is useful is a scene where a marker
  moves in the shadow of an actress. Previously it would not be possible
  to track such a situation, scale adaption would shrink the area to
  compensate for the change in illumination, losing the track. With
  "Normalize" turned on, the patch is correctly tracked and scale is
  maintained.
  Correlation is now a single value for all tracking settings and defines the minimal correlation between a matched pattern and a
  reference to be considered a successful tracking. If the tracker is
  giving up too easily, decrease this value, or if the tracker is
  slipping too much when it should give up sooner, increase this value.
  


Note that it is possible to simulate the old Hybrid tracker with the current method:


  To get behavior that is almost identical to the Hybrid tracker in
  previous Blender versions, enable Prepass and set the motion model to
  Location only.


E.g: